Microstructural characteristics and corrosion resistance of atmospheric pressure chemical vapor deposited SiO2 films from TEOS and O2

Chemical vapor deposited SiO2 films from tetraethyl orthosilicate (TEOS) is a key enabling material in numerous applications. Among the several pathways for the CVD of SiO2 films from TEOS, the poorly investigated medium temperature process involving oxygen ensures a compromise between the high thermal load of the surface reaction of the TEOS pyrolysis process, and the strong activation of gas phase reactions in the ozone assisted decomposition of TEOS. It is a promising route towards conformal coverage of complex-in-shape structures, growth rate control, and appropriate physical & chemical properties of the coating. SiOx films are obtained from TEOS+O2 in a horizontal CVD reactor operating at atmospheric pressure between 350 and 500°C. FTIR operating under normal and 55° incidence angle is used for the investigation of the structure, namely density, strain, oxygen content and stoichiometry of the films, by probing vibrational modes in the 900-1300 cm-1 region with well-resolved TO-LO phonon splitting. Complementary density values obtained by ellipsometry allow estimating the porosity of the films. Their corrosion resistance is investigated by the P-Etch test through thickness loss and is correlated with their composition, porosity and density

Silice amorphe, élaborée par CVD à partir de TEOS et O2 : Composition, stœchiométrie, structure et résistance à l’abrasion chimique

Depuis les années 80, l’élaboration de couches minces de silice, SiO2 à partir d’orthosilicate de tétraéthyle ((Si(OC2H5)4, TEOS) par dépôt chimique en phase vapeur (CVD) a été largement étudiée pour répondre aux problématiques de la microélectronique. Récemment, l’élargissement de l’éventail d’applications pour les revêtements à base de SiO2 pour l’optique, l’agroalimentaire, le biomédical, l’emballage ou la séparation des gaz, induit une modification des cahiers des charges tant pour les matériaux que les procédés. Il est souvent mis en avant les besoins de : (a) réduire le budget thermique lors de l’élaboration, (b) éliminer la formation de poudres, induites par exemple par une réactivité élevée en présence d’ozone, (c) revêtir des structures complexes, ce qui diminue l’intérêt des procédés plasma. En réponse à ces besoins, cette étude s’intéresse à la structure de couches de SiO2 amorphe élaborées à partir de TEOS et oxygène à pression atmosphérique à des températures Td comprises entre 400°C et 550°C, et corrèle ces caractéristiques à leur résistance à l’abrasion chimique

Investigation of the densification mechanisms and corrosion resistance of amorphous silica films

The barrier properties of the technologically attractive amorphous silica films depend on their structural characteristics at the atomic level, which, in turn are strongly influenced by the deposition conditions. In this paper, we propose an investigation of the poorly investigated densification mechanism of amorphous SiO2 films processed by CVD from TEOS and O2 between 400 and 550 °C. Based on literature survey and our original experimental results, we show that the densification process of these films, occurring with increasing the deposition temperature, is highlighted by a decrease of the water and silanol content, probed by transmission FTIR. We discuss the evolution of Si-O-Si related vibration signatures and we use the central force model to correlate the LO2 and LO3 shifts with the decrease of the Si-O-Si bond force constant, when the deposition temperature increases. Nuclear analysis reveals that films processed below 525 °C present hydrogen content between 5 ± 0.3 and 7 ± 0.3%at. Ellipsometry measurements attest that films processed at 550 °C are close to O/Si silica stoichiometry and hydrogen free. We show that application of the P-etch test results in particularly low erosion rate of 10 Å.s−1 for dense films processed at 550 °C

Tungsten carbides and nitrides supported on natural polymers-derived carbons for One-pot hydrogenolysis of cellulose to diols

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Cellulose conversion to glycols over DUT-8(Ni) derived nickel-tungsten/carbons: selectivity tuning.

International audienceThere have been various studies on the transformation of cellulose to low carbon polyols (C2,3), ethylene glycol (EG), propylene glycol (PG) and glycerol (Gly), which are prevailing intermediates in the manufacture of plastics, pharmaceuticals, food additives, and cosmetics, etc. Cellulose conversion to diols mainly involves 3 types of reactions: cellulose hydrolysis, retro-aldol condensation, and hydrogenation. For the formation of 1,2-PG, the sugar isomerization reaction is also involved. Using activated carbon-supported tungsten carbide (W2C/AC) catalysts, Zhang et al. obtained an EG yield of 76 % starting from cellulose [1]. Besides being a cheap non-noble metal-derived phase, a noteworthy advantage of tungsten carbide over other tungsten species (oxides and metal) is the preferential formation of EG among other polyols due to its Pt-like catalytic behavior. Yang et al. prepared Ni-W/C nanofiber catalysts, in situ fabricated through the pyrolysis of Ni, W-containing metal-organic framework fibers. A large productivity varying from 15.3 to 70.8 molEG.h-1.gW-1 was reported, which is two orders of magnitude higher than previously reported Ni-W-based catalysts [2]. Interestingly Sun et al. [3] showed the impact of the Sn phase and valence on the catalytic properties of bimetallic systems supported on activated carbon. When powder of metallic Sn was used with Ni/AC, a Ni-Sn alloy formed which promoted retro-aldol cleavage and hydrogenation, finally favoring EG production (58 %). When SnO was used, the catalyst promoted glucose isomerization, leading preferentially to PG (32 %). The above studies inspired our current work. A series of W and Ni-containing metal-organic frameworks were constructed by one-pot assembly of DUT-8(Ni) MOF precursors and Na2WO4·2H2O. A subsequent pyrolysis of the W@ DUT-8(Ni) materials at 700 °C under nitrogen produced nickel-tungsten/carbon catalysts. The following nomenclature was adopted for the resulting materials: NiW-l-x-C-N2; where x (nW/nNi) was set at 0.06, 0.12, 0.3, and 0.43, respectively. Figure 1 displays the catalytic results of the as-synthesized materials in the cellulose hydrogenolysis at 245 °C in a reaction time of 1 hour. Both materials with low (NiW-l-0.06-C-N2) and high (NiW-l-0.3-C-N2) W content were selective to EG (17 %). A remarkable yield switch to PG (36 %) was obtained at an average W loading (NiW-l-0.12-C-N2). The highest EG molar yield (25 %) was obtained over NiW-l-0.43-C-N2

New insights on the catalytic reductive amination of hydroxyacetone amination over RUWXC/AC Catalyst

International audienceThe production of chemicals and liquid fuels from renewable and non-edible lignocellulosic biomass has been considered as a promising way to reduce our dependance to fossil resources as well as to reduce CO2 release. Especially, nitrogen-containing molecules, particularly primary amines, are broadly used for the synthesis of pharmaceuticals, polymers, surfactants, agrochemicals, and dyes[1]. Owing to the high O/C ratio (~1/1) in biomass feedstocks[2], the production of oxygenates from biomass is rather straightforward and has been largely studied. However, the further production of valuable nitrogen-containing products is far less evident due to the deficit of efficient amination strategies of oxygenates. One way is the amination of aldehydes and ketones to primary amines, employing ammonia as the nitrogen source[3]. Due to the development of biorefining, renewable aldehydes and ketones including glycolaldehyde, glyceraldehyde, hydroxyacetone, and aromatic compounds are nowadays available at large scales, opening new opportunities to produce nitrogen-containing compounds[4]. For example, Liang et al. reported the use of partly reduced Ru/ZrO2 for the reductive amination of different biomass-based aldehydes/ketones in aqueous ammonia[5]. Despite this encouraging development, effective heterogeneous catalytic systems that allow the amination reaction to take place under milder conditions (T < 100 °C, P < 50 bar, aqueous phase, and without additives) with high amines’ yields are still lacking. In particular, the production of large-market amino alcohols from hydroxyacetone hasn’t been reported so far.Herein, we report the preparation of a highly efficient and robust catalyst, RuWxC/AC, for the reductive amination of hydroxyacetone (Figure 1). By varying several process parameters including time, temperature, the nature of nitrogen source, and pressure, up to 60 mol.% amines’ yield has been obtained. The promoting effect of tungsten carbide nanoparticles has been particularly investigated. Finally, a kinetic study has been conducted and will be discussed

Edge passivation of shingled poly-Si/SiO

This work aims at the full recovery of efficiency losses induced by shingling double-side poly-Si/SiOx passivated contacts crystalline silicon solar cells. It focuses on thermally-activated Aluminium Oxide (AlOx) layers elaborated by thermal Atomic Layer Deposition (ALD) to passivate the edges of shingled cells cut by using the innovative “45° tilt squaring approach”. The whole procedure featuring high-temperature AlOx annealing led to very low cut-related performance losses. Indeed, the efficiency and FF of the passivated shingled cells surpassed the values obtained for the as-cut shingles by 0.5%abs and 2.6%abs, respectively. Approaches for further improvements are also discussed, particularly to overcome the short-circuit current density decrease observed for passivated shingles